Effects of Mannitol on Rumen and Fecal Microbiome, Immune Function, and Antioxidant Capacity of Sunit Sheep

This study evaluated the effects of dietary supplementation with uncoated or coated mannitol on growth performance, rumen fermentation, rumen/fecal microbial communities, and serum immune and antioxidant indices in Sunit sheep. Twenty‐four healthy 7–8‐month‐old male Sunit sheep (28.84 ± 7.08 kg) were randomly assigned to three groups ( n = 8/group): control (CON; corn flour without mannitol), uncoated mannitol (UM; corn flour + 2 g/kg uncoated mannitol), and coated mannitol (CM; corn flour + 2.6 g/kg coated mannitol). After a 7‐day dietary adaptation period, all sheep were fed a uniform total mixed ration (TMR) for a 14‐day formal experimental period. The results indicated that neither uncoated nor coated mannitol supplementation significantly affected the average daily gain (ADG) ( p > 0.05). However, both treatments improved the gastrointestinal microbial structure and altered rumen fermentation, as evidenced by increased ruminal pH and decreased short‐chain fatty acid (SCFA) concentrations ( p < 0.05). For serum biochemistry, the UM group had higher total protein (TP), albumin (ALB), and creatinine (CREA) levels, and lower urea (UREA) levels ( p < 0.05); the CM group had higher TP and ALB, and lower UREA levels ( p < 0.05). Additionally, the CM group exhibited increased IL‐4, IgA, C3, SOD, and GSH‐Px levels, and decreased TNF‐β, IFN‐γ, and MDA levels ( p < 0.05). Correlation analysis revealed a strong negative correlation between serum TP and fecal norank_o__Gastranaerophilales abundance ( p < 0.01), and a negative correlation between IL‐4 and ruminal Christensenellaceae_R‐7_group abundance ( p < 0.05). In conclusion, both the mannitol forms reshaped ruminal and intestinal microbial structures and improved serum indices, with coated mannitol associated with more consistent improvements in immune and antioxidant indices.